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Bluefin

_Canada Underwater World 2

raditionally, the bluefin tuna It was 304 cm in length and 679 kg in T(Thunnus thynnus, L.) has been weight (Fig. 1). Bluefin Tuna considered one of the world's top sport The bluefin is generally dark, metal- fish. With its great size and power, in lic blue (nearly black) on the back, shad- addition to a streamlined body capable ing to silvery white or grey on the sides, of great bursts of speed, this spectacu- to white on the belly. Its somewhat lar fish is a sportsman's dream. The stout, fusiform (tapering toward either world record for rod-and-reel bluefin end) body, is nearly round in cross tuna has been established several times section, with a thin tail which is rigid, in Canadian waters. broad and crescent-shaped. Besides its The bluefin tuna is the largest mem- body form, other streamlining features ber of the family Scombridae. In order of the bluefin are its tightly closed jaws; to maintain a high level of activity, these smooth, flat gill covers; eyes that are fish are voracious eaters, feeding mainly "faired in"; and slots into which the fins on other fish. The scombrid family can be retracted. The second dorsal fin supports commercial and recreational and the anal fin are each followed by averaging 5 million tonnes per a row of 8 to 10 yellow, black-edged year. finlets leading to the base of the tail. It The are highly migratory and is thought that these may reduce turbu- therefore reside in the waters of many lence when swimming. The drawings in countries during their lives. Manage- Figure 2 illustrate the differences ment has been difficult and international between the bluefin and three other agreements must be sought for any tunas that occur off Canada's east effective controls. To assist in bringing coast. Figure 1. Largest bluefin tuna in the about such international management, Often referred to as "warm bodied", world. Landed at Auld's Cove, a number of bodies have been organ- bluefin are able to maintain their body N.S. on October 26, 1979, by ized. For the Atlantic, this body is the temperatures up to 10°C above that of Ken Fraser. Photo by Pat International Commission for the Con- the surrounding water. This is done McKinnon, Port Hawkesbury, servation of Atlantic Tunas (ICCAT) set through the use of a heat exchange sys- N.S. up in 1969. tem, which permits their muscles to The bluefin tuna is widely distributed, operate more efficiently in a much ranging throughout the Atlantic and greater range of water temperature than Pacific . It is highly esteemed in any of their prey species. This also the lucrative Japanese sashimi (fresh, enables them to move to different raw fish) markets for its high oil content climatic areas in search of food. and bright red flesh. World Distribution Description Bluefin tuna occur in the subtropical Because of their wide distribution, and temperate waters of the northern bluefin tuna have many different com- Atlantic and Pacific oceans as well as mon names. In Canadian waters alone, the Mediterranean and the Black seas. they are referred to as horse , In the Atlantic, they are found from great , tunny, and black fish. Labrador and Newfoundland in the Bluefin are one of the fastest fish in the northwest through the Gulf of Mexico world, capable of bursts of between 70 and the Caribbean to Brazil. In the east, to 88 km per hour. This speed, coupled they are found from to the with their large size, has made them one Mediterranean. Some catches have been of the most esteemed gamefish in the reported off South Africa although world. Canada was the home of the these may have been the southern blue- international Tuna Cup Match, held off fin tuna which is a different species, western Nova Scotia, between 1937 and occurring in the southern oceans. 1976. Now, North Lake, P.E.I. is The migrations of bluefin can be known as the Tuna Capital of the among the most extensive of any fish. World. The largest bluefin caught to Their movements appear associated with date (1985) was landed in 1979 in Auld's water temperature, spawning habits, Cove, N.S. in the Gulf of St. Lawrence. and the endless pursuit of prey. Larger bluefin tend to travel further than smaller individuals. Thus, at the Underwater World 3

extremes of their range, larger fish tend Thunnus thynnus Bluefin tuna (Eng) Thon rouge (Fr) to dominate in numbers. They are nor- mally gregarious, travelling in schools ranging from a few large bluefin to SIZE: many thousands of smaller fish. For the Maximum: over 300 cm first few years of life these fish school according to age and size. Common: 40 to 200 cm Tagging studies and trace-element analysis of vertebrae have indicated a limited exchange of fish between the east and west Atlantic. Returns from tagging studies indicate some individual fish have travelled up to 8,000 km in 50 days.

Canadian Distribution Thunnus alalunga Albacore (Eng) Germon (Fr) Adult bluefin return to Canadian waters after spawning in the Gulf of Mexico. Although at present only "giants" (greater than 140 kg) occur SIZE: in Canadian waters, prior to the early Maximum: 120 cm 1960s there were two size-classes. The Common: 40 to 110 cm smaller class, referred to as "jumpers" (20 to 70 kg) arrived later (late August) and left earlier than the giants which tended to arrive in June and leave in October or November, depending on water temperatures. The disappearance of jumpers is thought to be due partly to heavy fishing of the smaller sizes in Thunnus albacares (Eng) Albacore (Fr) the early 1960s and partly due to environmental factors. Migration patterns for bluefin in SIZE: Canadian waters have apparently Maximum: 190 cm changed over time. The controlling Common: 40 to 170 cm influences of such changes are not fully understood although environmental conditions and availability of prey are known to be major factors. There may also be a degree of homing in various stocks. The appearance of bluefin in any area is thought to depend to a large extent on the local movement of prey species such as mackerel and . The earliest bluefin arrive off Nova Thunnus obesus (Eng) Thon obese (Fr) Scotia's coast in June and July, and by late July they are seen as far north in the SIZE: Gulf of St. Lawrence as Chaleur Bay. Maximum: 190 cm Fishing continues until late October Common: 40 to 170 cm when the stock begins to move out of the Gulf. The last stop is often St. Georges Bay, N.S. before the final departure, presumably back to tropical waters for spawning.

Figure 2. A comparison of bluefin and three other tunas that occur off Canada's east coast (reproduced from FAO Species Catalogue, Volume 2: Scombrids of the World). Underwater World 4

World Tunas and support both commercial and recreational fisheries around the world. Prime fishing areas include the southwestern and eastern tropical Pacific, and the eastern tropi- cal Atlantic. Much of the commercial fishery is taken by "distant water" fisheries (i.e. boats that range widely from their home ports). Small tunas and mackerel are landed by purse seiners (Fig. 3), drift netters, pole and line boats, longliners and trap nets. The larger members of the tuna family are generally caught by long- lining, trolling, and trap nets. The total worldwide tuna catch aver- ages about 5 million tonnes a year with Figure 3. Purse seiner off the U.S. coast in 1981 fishing for small tuna a recent peak of 6 million tonnes in species for the North American market. Photo by Tom Hurlbut, 1978. The world catch for bluefin tuna DFO, Moncton. is considerably less, ranging between 35,000 and 45,000 tonnes. The Atlantic bluefin portion constitutes approxi- mately half of this catch; the Canadian portion is very small, not exceeding 700 tonnes a year in the last decade (Table 1). The U.S. and Japan have the largest Table 1 tuna catches and markets in the world. West Atlantic Landings Japan is the largest in terms of the blue- fin, with the greatest part of the world's YEAR Canada Canada Canada U.S.A. Japan TOTAL catch (including Canada's) sold on its gear: TRAP HAND PURSE domestic fresh and frozen fish market.

1970 130 151 1200 3800 100 5700 Canadian Fishery 1971 59 88 900 4100 1400 6900 Canadian fishing for tuna began at 1972 29 188 300 3100 300 4100 the turn of the century off Nova Scotia. 1973 144 239 600 1600 1100 4100 This sport fishery shifted as yearly 1974 256 407 100 1600 900 3500 migration patterns changed and as 1975 144 203 300 2900 1500 5200 widespread interests in sport fishing 1976 172 341 300 1900 2900 6000 increased. The first tuna fishing in 1977 368 301 300 2100 3700 6800 Newfoundland waters began in 1957 in 1978 221 208 200 1900 3100 5900 Conception Bay and spread in later 1979 31 214 0 2300 3600 6500 years to Notre Dame Bay. Tuna fishing 1980 47 259 0 1600 3900 5900 in the Gulf of St. Lawrence (in recent 1981 41 279 100 1400 3800 5900 years, the mainstay of the fishery in 1982 68 223 0 600 300 1400 Canada) was first developed off Prince 1983 7 426 0 1300 700 2500 Edward Island in 1967, and was devel- 1984 3 261 0 1200 700 2200 oped in Chaleur Bay in 1973 and 1985 10* 130* 0 — 2660 (TAC) St. Georges Bay in 1978. Historically, the Canadian tuna fish- * provisional eries have used five major gear types: sport rod and reel, purse seine, trap net, The landings by weight (tonnes) from the western Atlantic . The Canadian trap harpoon, and incidental catches on net fishery is from St. Margarets Bay, N.S. Landings from other areas include fish longlines and in gillnets. Neither purse taken by all gear types used. The total catch does not tally with the other columns seines nor harpoons remain in use of the table as unclassified gear has been included in the total. (Most of the values today. Since 1980, an increasing number in this table have been rounded to the nearest 100 tonnes.) of fishermen have used a new method Underwater World 5

Some bluefin may reach maturity as early as four years of age or 25 kg in size but the main spawning component involves fish of 10 years and older. The number of eggs produced range from 5 million for small individuals to 60 mil- lion for the "giants" (over 15 years of age). Early development of the eggs and larvae is rapid. The eggs, buoyed by an oil droplet, float just below the water surface and hatch within a few days. During this time they are prey to many fish and invertebrate species. Within three months, the young bluefin can weigh more than a half kilogram and by Figure 4. The final round-up of tuna in an impoundment of a the end of their first year, 4 kg. For the ranching operation in St. Margarets Bay, N.S. Photo by first four to five years of life they double Bill McMullon, DFO, St. Andrews. their weight annually. Age and Growth Little work has been completed on age and growth studies of bluefin tuna. called "tended line" or "keg" fishing, What has been done indicates they live which involves a single hook on a length to a relatively old age. The oldest of buoyed rope tied to the vessel. recorded age in Canadian waters is The catch of bluefin from the mack- 38 years. The Canadian fishery now erel trap fishery was considered inci- exploits mainly fish ranging in age from dental until 1974 when the first tuna 15 to 30 years. The average age and size holding cages (or pounds) were set up of fish in this fishery have been increas- in St. Margarets Bay. This ranching ing over the last few years as a result of operation grew steadily until 1979 when the reduced recruitment to the older ages 948 tuna were fattened in these due to the heavy fishing effort on the impoundments (Fig. 4). Since then, juveniles in the 1960s. there has been a decline to a total of only Bluefin grow rapidly during their eight fish harvested in 1984. first 12 years or until they reach about Currently, the only major gear com- 250 cm in length, after which the proc- ponents of the Canadian tuna fishery ess slows (Fig. 5). There is no difference are rod and reel (both sport charters and in the weights of males and females of operations) and the same length (Fig. 6). However, tended line. The tended line gear is males tend to grow longer and therefore increasingly popular for several reasons: heavier, while females appear to live first, the price of fuel has increased longer. markedly in the last decade making The migration to Canadian waters is trolling with rod and reel more expen- definitely for feeding purposes. When sive; secondly, the tended line can be the tuna first arrive after their winter used in conjunction with other gears (i.e. spawning in the Gulf of Mexico they are herring or groundfish gillnetting); and lean, with a low oil content. Therefore, thirdly, the catch-per-unit effort (fish- the bluefin caught in the earliest part of ing days) is nearly double that of rod the fishing season are worth much less and reel. on the Japanese sashimi market than those caught later in the season. The fish Fecundity and Spawning increase in weight by up to 2 kg per day Atlantic bluefin spawn in the during their time in northern Canadian and the Gulf of waters. This is strictly a "fattening" Mexico. These two spawning concentra- process as it occurs without a corres- tions are the basis of the two-stock ponding increase in length. concept (i.e. east and west Atlantic). Underwater World 6

Feeding studies in Canadian waters 270 are somewhat biased as samples come from the commercial fishery which is

) 240 largely nearshore (i.e. less than 16 km off the coast). Because of this, inshore

(cm 210 species of prey tend to predominate in 180 the stomach samples. During the life of 150 the bluefin, are probably the most important food source as they are found LENGTH 120 in the offshore slope areas of the Atlantic as well as in nearshore regions. 90 Data collected from fish caught off 60 Prince Edward Island in 1983 indicated heavy feeding on herring — up to 30 50 herring in a specimen's stomach at a time. Additional prey included squid, 3 6 9 12 15 18 21 24 27 mackerel, , and white hake. AGE Other marine compete with Figure 5. Mean age at length of the bluefin tuna recorded from Canadian young tuna for food resources and some waters from 1975-85. prey upon the tuna at various stages of its life. The only likely predators of mature bluefin would be the toothed Food and Feeding whales and large . The majority of data on the feeding Utilization habits of large bluefin has been collected Although most species of tuna are in Canada and northern Europe. Studies canned, bluefin are usually marketed from these areas indicate that pelagic fresh or frozen. Normally, bluefin are fish (herring, mackerel, ) are the canned only when small or medium- major prey. The tuna's rapid growth in sized individuals are caught mixed with weight during the northern summer schools of other tuna. Like other long- feeding season, coupled with its warm lived species, bluefin accumulate mer- body temperature which increases the cury with age. The larger fish generally rate of digestion, indicates that tuna are exceed U.S. and Canadian mercury con- important predators, and that bluefin tent standards and hence are not sold in probably make a significant ecological impact in the Gulf of St. Lawrence. Canada. Japan is the largest market in the world for fresh and frozen tuna. Most Figure 6. Mean weight at length of bluefin tuna recorded from Canadian of their bluefin is consumed as raw, waters from 1975-85. thinly-sliced meat in sushi and sashimi dishes. Bluefin tuna is the most desira- I I I ble tuna species in Japan, followed by 900 bigeye and yellowfin. Between 1980 and 800 1984, the prices paid to Canadian fisher- men at the wharf for bluefin have fluc- 700 tuated between $1.00 and $2.50 per ) 450 g. However, the price reached $5.50

kg 600 ( per 450 g for a brief period in 1984. In T 500 Japanese restaurants, the choicest blue-

GH 400 fin sashimi may sell for as much as $50.00 per 450 g. WEI 300 Since the flesh is eaten raw, the qual- 200 ity of bluefin must be excellent. The main sashimi price determinants are 100 freshness, fat or oil content and colour • of the meat. To ensure that bluefin fetch 50 80 110 140 170 200 230 260 290 a premium price in the Japanese market- place, processors must meticulously LENGTH (cm) Underwater World 7

clean, chill and package the carcasses fork length, and round weight of the for shipment. The carcasses should be fish; date, location, and method of chilled in brine until their core temper- capture; and the name and address of atures are depressed to 5°C or lower; the fisherman (for the reward). this frequently requires 20 to 30 hours. Prior to shipment, the carcasses are Management: International drained, washed and inspected before Fishing for was being placed in individual, plastic-lined unregulated before the formation of wooden boxes with bagged ice. ICCAT in 1969. Even at this time it was The carcasses are shipped in refriger- feared that too many juveniles were ated transport trucks to New York City being fished. Thus, in 1975, the first where they are loaded onto cargo planes bluefin regulation came into effect for the flight to Tokyo. Total turn- establishing a minimum size and limit- around time from wharf to market is ing the level of fishing intensity to that three to four days. of the early 1970s. These regulations were extended over Research the next seven years until it became obvi- Research in Canadian waters has been ous that limiting the fishing levels to based largely on samples taken from the those of the early 1970s was not enough commercial fishery, and has been to halt the "alarming decrease in abun- directed towards age and growth, food dance" noted in the west Atlantic. As and feeding, and morphometrics (body a result, the first of a series of quotas measurements) for stock discrimination was introduced in 1982. This limited the studies (Fig. 7). total west Atlantic catch to 1,160 tonnes International tagging studies have (Canada 250 tonnes, Japan 305 tonnes, attempted to define the movement and U.S. 605 tonnes) and prohibited direct- distribution of bluefin in the Atlantic. ed fishing on the spawning grounds of They also provide information on the Gulf of Mexico. growth. Canada was active in this pro- It was found that the biological infor- gram, and tagged fish are still being mation gathered from this limited fish- recovered up to 20 years later. People ery was not sufficient to allow scientists who find a tag are asked to return it to to assess the stock. Therefore, the quota the nearest DFO fisheries officer with was raised in 1983 to 2,660 tonnes the following information: lower jaw/ (Canada 573 tonnes, Japan 699 tonnes, U.S. 1,387 tonnes). This quota and ear- Figure 7. "Billie" Burnett, DFO, sampling a giant bluefin tuna for commer- lier regulations, including minimum size cial statistics in St. Margarets Bay. Photo by Frank Cunningham, and the prohibition of fishing on spawn- DFO, St. Andrews. ing grounds in the Gulf of Mexico, are still in effect as of the 1986 fishing season. Management: Canadian In Canadian waters, the Department of Fisheries and Oceans manages the stock within ICCAT guidelines. The department converts the Canadian quota into numbers of fish (1,521 in 1986) based on average weights from previous years and then allocates them by area among the major fishery com- ponents. By mid-season, it re-adjusts the allocations if some areas appear unlikely to reach their quotas. Underwater World 8

Canada also has introduced several Further Reading: Underwater World factsheets are brief additional measures for the fishery Butler, M.J.A., "Plight of the Bluefin illustrated accounts of fisheries within its waters. These include restric- Tuna." National Geographic, resources and marine phenomena pre- tions on the number of licences issued, August 1982, pp. 220-239. pared for public information and edu- the number of fish landed per day per Collette, B.B. and C.E. Nauen. 1983 cation. They describe the life history, boat, and the types and quantity of gear. FAO Species Catalogue, Volume 2: geographic distribution, utilization and It is hoped that the stocks of Atlantic Scombrids of the World. FAO population status of fish, shellfish and bluefin tuna will rebuild over the next Fisheries Synopsis No. 125. 137 other living marine resources, and/or decade and that, with good manage- pages. the nature, origin and impact of marine ment, the long-term average catch will International Commission for the processes and phenomena. double or triple. Conservation of Atlantic Tunas. Collected Volumes of Scientific Papers, Volumes 1-23, 1971-85. (Available through libraries.)

Text: Douglas Clay and Tom Hurlbut Marine Fisheries Division Dept. of Fisheries and Oceans P.O. Box 5030 Moncton, N.B. E1C 9B6

Published by: Communications Directorate Fisheries and Oceans Ottawa, Ontario K1A 0E6 Others in this series: American Atlantic Snow Sand Lance DFO/1898 UW/55 American Capelin Lumpfish Sea American Smelt of the Marine Fish Eggs Selected Arctic Charr Atlantic Coast and Larvae Selected Minister of Supply and Services Arctic Cod Dungeness Crab Northern of British Columbia Canada 1986 Grey Seal Soft-Shell Clam Catalogue Number Fs 41-33/55 Atlantic Groundfish Harbour Seal Pacific Herring Spiny Dogfish Atlantic Harp Seal Pacific Thorny and Smooth Skates — 1986E Atlantic Herring Hooded Seal () ISBN 0-662-14550-X Atlantic Mackerel Irish Moss Redfish White Hake Atlantic Lake Red Hake Winter Lingcod Red Tides Flounder Disponible en francais Atlantic Shellfish Roundnose Grenadier